Conventional television special-effects generators are capable of achieving a wide variety of linear, circular, elliptical and rotational wipes and multiple-image-segment effects. A sophisticated conventional special effects generator, for example, can easily extract a circular central portion from one incoming signal-borne image and substitute or switch it for a second incoming signal-borne image in such a manner that the diameter of the circular central portion may be freely varied. See, for example, the special-effects generator which is disclosed in U.S. Pat. No. 3,758,712 which issued on Sept. 11, 1973 to John P. Hudson.
A shortcoming of such conventional generators is their inability to reposition an image segment within an image. For example, if a video signal is conveying an image that contains a man's face in the upper left-hand corner of the conveyed image, there is no way that a conventional special-effects generator can rotate, alter the size of, or reposition the man's face within the conveyed image. For example, the man's face cannot be shifted to the center of the conveyed image by a conventional special-effects generator. This shortcoming remains regardless of how sophisticated the conventional special-effects generator may be in other respects.
Optical and mechanical techniques may be used to reposition, rotate, and alter the size of image segments before the segments are impressed upon a video signal. For example, image rotation may be achieved by utilizing a Pechan prism and image size adjustment can be achieved by utilizing a zoom lens. These mechanical techniques are not easily controlled digitally, however, and they lack flexibility. Many effects easily achievable using the present invention could only be achieved with great difficulty, if at all, using a mechanical optical system of great complexity.
Computers have been used successfully to digitize video information and subsequently to manipulate the digitized data for modifying the video image; however, those systems are very expensive and limited in their applications due to cost and the size of the computer required.